Smoking articles, particularly cigarettes, generally comprise a tobacco rod of shredded tobacco (usually, in cut filler form) surrounded by a paper wrapper, and a cylindrical filter aligned in an end-to-end relationship with the tobacco rod. Typically, the filter includes a plug of cellulose acetate tow attached to the tobacco rod by tipping paper.
Upon lighting a cigarette, a smoker draws mainstream smoke from the lit end of the cigarette. The drawn cigarette smoke first enters the upstream end portion of the filter and then passes through the downstream portion adjacent the buccal end of the cigarette, upon which the user draws the smoke.
To achieve appropriate filtration efficiency, materials such as carbon have been incorporated into cigarette filters. A current method for incorporating adsorbent materials in cigarette filters is the physical entrapment of adsorbent particles between cellulose acetate (CA) fibers. An improved and more expensive design is to put certain materials in the cavity between CA plugs in a predetermined configuration, such as a plug-space-plug filter configuration, to limit the exposure of adsorbent to the triacetin binder.
Certain cigarettes incorporate filter segments with adsorbent materials such as activated carbon to achieve desired filtering characteristics. Examples of such filters are described in U.S. Pat. Nos. 2,881,770 to Tovey; 3,353,543 to Sproull et al.; 3,101,723 to Seligman et al.; and 4,481,958 to Ranier et al. Certain commercially available filters have particles or granules of carbon (e.g., an activated carbon material) alone or dispersed within a CA tow. Other commercially available filters have carbon threads dispersed therein; while still other commercially available filters have so-called “plug-space-plug”, “cavity filter” or “triple filter” designs. Examples of commercially available filters are SCS IV Dual Solid Charcoal Filter and Triple Solid Charcoal Filter from Filtrona International, Ltd.; Triple Cavity Filter from Baumgartner; and ACT from Filtrona International, Ltd. Detailed discussion of the properties and composition of cigarettes and filters is found in U.S. Pat. Nos. 5,404,890 and 5,568,819, both to Gentry et al, the disclosures of which are hereby incorporated by reference.
Cigarette filter elements which incorporate carbon have the ability to remove constituents of mainstream smoke that pass therethrough. In particular, activated carbon has the propensity to reduce the levels of certain gas phase components present in the mainstream smoke, resulting in a change in the organoleptic and toxicological properties of that smoke.
It would be desirable to provide a cigarette having a cigarette filter incorporating carbon and/or other materials capable of absorbing and/or adsorbing gas phase components present in mainstream cigarette smoke, while providing favorable absorption/adsorption, dilution and drawing characteristics, so as to enhance consumer acceptability.
Furthermore, commercially available activated carbons and molecular sieves are typically in granular and powdered forms. Materials in these forms do not maintain product cohesion, as granules or grains tend to settle after being packed inside a cigarette filter. It is therefore desirable to form rod-shaped, channeled, activated carbon articles, such as monolithic tubes, for use in cigarette filtration to achieve lower resistance to draw, higher total particulate matter delivery, and better product integrity.